Recently, from the viewpoint of energy saving or environmental conservation, illumination devices (such as LED bulbs or LED fluorescent lamps) using a light emitting diode (LED) as a light source have been used instead of incandescent lamps or fluorescent lamps.
However, a conventional illumination device using an LED as a light source can emit light only in the forward direction but cannot emit light in all directions like an incandescent lamp Or a fluorescent lamp. Accordingly, the conventional illumination device cannot extensively illuminate a room using reflected light from a ceiling or walls.
In order to make light distribution characteristics of such a conventional illumination device using an LED as a light source close to the light distribution characteristics of an incandescent lamp or a fluorescent lamp, it has been proposed that the traveling direction of light emitted from the LED is controlled by the use of a light flux controlling member (for example, see Patent Documents 1 to 3).
FIG. 1 is a diagram illustrating the configuration of a light direction converting element (light flux controlling member) described in Patent Document 1 . FIG. 1A is a plan view of the light direction converting element and FIG. 1B is a cross-sectional view taken along line A-A of FIG. 1A. As shown in the drawing, light direction converting element 101 reflects light from LED 100 by the use of surface B (paraboloid of revolution) 102 and surface E (beveled inclined surface) 103, further reflects the light reflected by surface B 102 and surface E 103 by the use of surface D 104 (the surface of a board having LED 100 mounted thereon), and emits the light reflected by surface D 104 from surface B 102. Light direction converting element 101 emits the light reflected by surface B 102 and arriving at surface C 105 to an external oblique rear side (downside).
By controlling the traveling direction of light from LED 100 by the use of light direction converting element 101, it is possible to obtain emitted light in the upward direction (forward direction) and the horizontal direction (the direction perpendicular to the forward direction). Therefore, it can be thought that the light distribution characteristics are made to be close to the light distribution characteristics of an incandescent lamp or a fluorescent lamp, by applying the light direction converting element 101 to the conventional illumination device using an LED as a light source.